The present invention relates to structure stabilizing systems, and more particularly to a vibration damping system for removing vibrations from a structure using piezoceramic actuators.
Vibration has historically been recognized as a problem which can produce a variety of adverse effects in equipment. Special precautions are needed to protect machine elements of air-borne laser tracking systems. The task of damping such undesirable vibration in the structure of the optical bench, while minimizing the impact on the existing design, has been alleviated, to some extent, by the following U.S. Patents, which are incorporated herein by reference:
U.S. Pat. No. 2,443,471 issued to Mason on 15 Jun. 1948;
U.S. Pat. No. 2,964,272 issued to Olson on 13 Dec. 1960;
U.S. Pat. No. 3,464,657 issued to Bullard on 2 Sep. 1969;
U.S. Pat. No. 3,703,999 issued to Forys et al on 28 Nov. 1972;
U.S. Pat. No. 4,795,123 issued to Forward on 3 Jan. 1989; and
U.S. Pat. No. 4,849,668 issued to Crawley et al.
All of the references cited above disclose systems for controlling mechanical vibration. The Mason reference discloses a damping assembly which uses a pair of piezoelectric crystal plates as a damping means. The approach of applying dynamically responsive damping elements is superior to mechanical mounting solutions such as springs, dash pots and other vibration absorbing mountings.
The Olson and Bullard references provide a vibration controlling apparatus containing a vibration sensing element, an amplifier, and a driving element. The driving element translates the amplified electrical signal into mechanical force to compensate for vibration.
Crawley et al teach that problems associated with the encapsulation and embedment of piezoceramic elements in a conductive matrix may be resolved by selecting a polymide material as insulation and enshrouding the elements with such material using a hard adhesive resin. As indicated in col. 1, lines 36-38, the use of piezoelectric elements for the purpose of electrically controlling resonance modes has been practiced on a macro scale without any consideration being given to micro scale or miniaturization. In this regard, note the particular embodiments set fourth in col. 2, lines 56-59. Crawley et al are clearly devoid of any teaching that the piezoelectric elements together with the sensor and control elements can be integrated in a miniaturized patch with little or no interface requirements, thereby opening the door to spacecraft application. The present problem requires a vibration damping system capable of responding to components of vibration produced by both acceleration as well as velocity of the host aircraft and neither of the above-cited references accomplish both velocity and acceleration nulling.
The Forys et al reference discloses a wideband stabilizing system for stabilizing cameras on moving vehicles. The stabilizing system includes a mounting system which houses the camera, as well as damps motion induced vibration. However, for the present problem, it is preferred to use the existing optical bench, rather than construct a new platform. Therefore, a vibration damping system is needed which may be attached to existing structures, as suggested by the Forward patent.
Much attention in past vibration suppression efforts has been given to the encapsulation and subsequent embedment of piezoceramics and other materials as actuators in composite materials. These actuators were used in conjunction with embedded sensors to perform active vibration control. There has been little attempt so far at miniaturizing the power and control electronics associated with the vibration control or incorporation of all components into a modular, self-contained entity-smart patch. Also, in past efforts, the assumption has been made that from +200 to +400 volts are readily available. This will probably not be the case on a spacecraft where the eventual size of the smart patch will be bounded by at least three variables--cost, volts required and volume available.
The preceding discussion indicates that there is a need for vibration suppression and shape control of structures using bonded piezoceramic sensors and actuators in conjunction with miniaturized control electronics. The present invention is intended to satisfy that need.